Preparation of high purity chromium and other metals



United States Patent Ofiice Patented Aug. 8, 1961 2995 '43s PREPARATION or their PURITY CHROMIUM AND ornnn METAIS Lawrence M. Litz, Lakewood, Ohio, assiguor to Union Carbide Corporation, a corporation of New York No Drawing. Filed Feb. 2, 1959, Ser. No. 790,390 11 Claims. (Cl. 75-434) This invention relates .to the purification of certain metals, and more particularly relates to a process of purifying metals utilizing a novel scavenging compound, thereby decreasing the impurity content and subsequently improving the metallurgical properties of such metals.

The hardness and ductility of metals are generally dependent upon their impurity content in addition to the inherent properties of the metals themselves. It would be greatly advantageous to purify certain metals, such as chromium and vanadium, thereby rendering them softer and occasionally more ductile than they are as presently available. Such improved ductility and softness will facilitate drawing, extruding, machining, and molding of such metals into desired shapes.

It is therefore the primary object of this invention to produce purer metals of the above-disclosed group than have been available in the past. It is another object of this invention to provide a novel process for the purification of such metals thereby rendering them softer and occasionally more ductile than has been formerly possible.

In accord with and fulfilling the above-mentioned objects, the invention comprises either heating a metal chosen from the group consisting of chromium and vanadium to an elevated temperature in the presence of cerium monosulfide, or heating the metal in question to an elevated temperature a d then placing cerium monosulfide in its presence. Broadly, the process of this invention may be carried out by heating such metal to above its melting point in contact with this compound.

Constant agitation at this elevated temperature may be beneficial in order to allow all of the metal to come into contact with the compound, thereby providing an inter face where purification occurs.

More particularly, the invention may be carried out by heating a metal from the above-disclosed group in a container made of cerium monosulfide to effect the escape of gaseous impurities from the metal without substantial reaction occurring between the metal and the container. A related method of purification encompasses adding the cerium monosulfide directly to a pool of the metal to be purified in the molten state. The mixture is desirably agitated for a given length of time, depending upon the impurity content of the metal and the temperature involved, and the purified metal is then recovered. It is important in the practice of any of the above-noted methods that the purification be carried out in a nonoxidizing inert atmosphere. Such an atmosphere may be provided by evacuating the system or by blanketing it with an inert gas such as helium or argon. Heating of the metal may be accomplished by induction heating through the compound if such is used as the container for the metal to be purified, or by any other convenient means which contamination of the metal by the heating element.

It is to be understood that the above discussion of chromium and vanadium applies equally as well to chromium and vanadium base alloys.

As specific examples of the practice of this invention, chromium has been purified by heating it in a cerium monosulfide crucible to various temperatures between 50 C. and 150 C. above its melting point for periods of from 5 to 32 minutes, under an argon atmosphere. The results of these test runs appear in summary form in Table A below.

TABLE A Chromium melted in CeS 5 Run I Run 11 Run III Superheat, O., above melt- 50 75 140.

tng p0 Duration, Minutes 30 32 5. Helium Pressure, mm. Hg 380 380 100. Surface Appearance. Sllvery Silver-Yellow.-. Gold.

Chemical Analysis Run I Run II Run III Before Impurity Purificatlon nil 0. 079 0.04 0. 017 0.004 0.007 0.039 nil 0.012 0.047 N.T. 0.76 0.013 N.T. 0.05 Hardness: Diamond Pyrami 637 174 N.T. 205

1 N.T.Not tested.

TABLE B 35 Hardness 0. Pressure, Metal Superheat mm. Hg Standard Purified DPH DPH Vanadium 60 1x10 259 190 Dlamond Pyramid hardness.

Metallographic examination of vanadium showed a very significant reduction in impurity occlusions.

What is claimed is:

.1. A process for purifying a material consisting of a metal selected from the group consisting of vanadium, chromium, vanadium base alloys and chromium base alloys which comprises heating said material in the presence of independently produced cerium monosulfide to a temperature above the melting point of said material, at such elevated temperature for a sufiicient' time to render said metal relatively ductile, and cooling said metal.

2. A process for purifying vanadium metal which comprises heating said material in the presence of independently produced cerium monosulfide to a temperature above the melting point of said metal, agitating said metal at such elevated temperature for a suflicient time to render said metal relatively ductile, and cooling said metal.

3. A process for purifying chromium metal which comprises heating said material in the presence of independently produced cerium monosulfide to a temperature above the melting point of said metal, agitating said metal at such elevated temperature for a sufiicient time to render said metal relatively ductile, and cooling said metal.

4. A process for purifying chromium base alloys which comprises heating said alloy in the presence of independently produced cerium monosulfide to a temperature above the melting point of said alloy, agitating said alloy at such elevated temperature for a sufiicient time to render said alloy relatively ductile, and cooling said alloy.

5. A process for purifying vanadium base alloys which comprises heating said alloy in the presence of independently produced cerium monosulfide to a temperature above the melting point of said alloy, agitating said alloy at such elevated temperature for a suflicient time to render said alloy relatively ductile, and cooling said alloy.

6. A process for purifying a material consisting of a metal selected from the group consisting of vanadium, chromium, vanadium base alloys and chromium base alloys which comprises melting said material in a cerium monosulfide crucible under an inert atmosphere, agitating said molten material, superheating such during said agitation and cooling said purified material.

7. A process for purifying vanadium metal which comprises melting said metal in a cerium monosulfide crucible under an inert atmosphere, agitating said molten metal, superheating such during said agitation, and cooling said metal.

8. A process for purifying chromium metal which comprises melting said metal in a cerium monosulfide crucible under an inert atmosphere, agitating said molten metal, superheating such during said agitation, and cooling said metal.

9. A process for purifying chromium base alloys which comprises melting said alloy in a cerium monosulfide crucible under an inert atmosphere, agitating said molten alloy, superheating such during said agitation, and cooling said alloy.

10. A process for purifying vanadium base alloys which comprises melting said alloy in a cerium monosulfide crucible under an inert atmosphere, agitating said molten alloy, superheating such during said agitation, and cooling said alloy.

11. A process for purifying chromium which comprises melting said chromium in a cerium monosulfide crucible under an inert atmosphere, agitating said molten chromium for from 5 to 32 minutes, superheating said molten chromium between 50 C. and C. above the melting point thereof during said agitation, and cooling said chromium.

References Cited in the file of this patent UNITED STATES PATENTS 1,869,496 Osborg Aug. 2, 1932 1,869,979 Osborg Aug. 2, 1932 2,101,919 Schichtel Dec. 14, 1937 2,509,189 Jordan May 23, 1950 2,624,667 Tour Jan. 6, 1953 2,670,284 Zvanut Feb. 23, 1954 2,759,723v Crespi Aug. 21, 1956 2,766,110 Meister Oct. 9, 1956 2,801,099 Larson Ian. 30, 1957 FOREIGN PATENTS 1312/36 Australia Nov. 30, 1936 

1. A PROCESS FOR PURIFYING A MATERIAL CONSISTING OF A METAL SELECTED FROM THE GROUP CONSISTING OF VANADIUM, CHROMIUM, VANADIUM BASE ALLOYS AND CHROMIUM BASE ALLOYS WHICH COMPRISES HEATING SAID MATERIAL IN THE PRESENCE OF INDEPENDENTLY PRODUCED CERIUM MONOSULFIDE TO A TEMPERATURE ABOVE THE MELTING POINT OF SAID MATERIAL, AT SUCH ELEVATED TEMPERATURE FOR A SUFFICIENT TIME TO RENDER SAID METAL RELATIVELY DUCTILE, AND COOLING SAID METAL. 